This invention relates to multilamp photoflash units and, more particularly, to an improved linear array of photoflash lamps.
Numerous multilamp arrangements with various types of sequencing circuits have been described in the prior art; particularly, in the past few years. A currently marketed photoflash unit (described in U.S. Pat. Nos. 3,894,226; 3,912,442; 3,935,442; 3,937,946; 3,941,992; 3,952,320 and 4,017,728 and referred to as flip flash) employs high voltage type lamps adapted to be ignited sequentially by successively applied high voltage firing pulses from a source such as a camera-shutter-actuated piezoelectric element. The flip flash unit comprises an elongated planar array of eight high-voltage type flashlamps mounted on a printed circuit board with an array of respectively associated reflectors disposed therebetween. The lamps are arranged in two groups of four disposed on the upper and lower half respectively of the rectangular-shaped circuit board. A set of terminal contacts at the lower end of the unit is provided for activation of the upper group of lamps, while a set of terminal contacts at the top of the unit is operatively associated with the lower group of lamps. The application of successive high-voltage pulses (e.g. 500 to 4,000 from, say, a piezoelectric source controlled by the shutter of a camera in which the array is inserted) to the terminal contacts at the lower end of the unit causes the four lamps at the upper half of the array to be sequentially ignited. The array may then be turned end for end and again inserted into the camera in order to flash the remaining four lamps. In this manner, one group of lamps (or half of the array) functions as a flash extender for the other group of lamps, so that only the group of lamps relatively farther from the camera lens axis can be flashed. The purpose of such an arrangement is to position the "active" group of flashlamps farther above the camera lens in order to reduce the possibility of a "red-eye" effect that causes the pupils of a person's eyes to appear red or pink in the flash pictures taken when the flashlamp is close to a camera lens.
The flip flash circuit board comprises an insulaing sheet of plastic having a pattern of conductive circuit traces, including the terminal contacts, on one side. The flashlamp leads are electrically connected to the circuit traces by means of eyelets secured in the circuit board and crimped to the lead-in wires. The circuitry on the board includes six printed, normally open, connect switches that chemically change from high to lower resistance so as to become electrically conducting after exposure to the radiant heat energy from an ignited flashlamp operatively associated therewith. The purpose of these switches is to provide lamp sequencing and one-at-a-time flashing. The four lamps of each group are arranged in a parallel circuit with three of the four lamps being connected in series with respective thermal connect switches. Initially, only the first of the group of four lamps is connected directly to the voltage pulse source. When this first group flashes, it causes its associated thermal connect switch (which is series connected with the next or second lamp) to become permanently conductive. Because of this action, the second lamp of the group of four is connected to the pulse source. This sequence of events is repeated until all four lamps have been flashed.
The overall construction of the flip flash unit comprises front and back plastic housing members with interlocking means for providing a unitary structure. The front housing member is a rectangular concavity, and the back housing is substantially flat. Sandwiched between the front and back housing members, in the order named, are the flashlamps, a unitary member, preferably of aluminum-coated plastic, shaped to provide the eight individual reflectors of the array, an insulating sheet, a printed circuit board, and an indicia sheet, which is provided with information trademarks and flash indicators located behind the respective lamps and which change color due to heat and/or light radiation from a flashing lamp, thus indicating at a glance which of the lamps have been flashed and not flashed. Each of the individual reflectors have a concave, generally parabolic, surface with the lamps being disposed within this concavity; the rear surface of the reflector has holes or slots to permit light and heat radiation to pass through for actuating circuit board switches and flash indicators. In order to provide electrostatic shielding for the lamps and circuitry, the reflector member is rendered electrically conductive by a reflective metalized coating thereon, and this coating is electrically connected to a common circuit conductor on the printed circuit board. Further, a metal foil is lamanated on the indicia sheet and also connected to this common conductor of the circuit board.
In U.S. Pat. No. 4,133,023, a flip flash array is illustrated which does not employ aluminizing on the reflector member and, thus, eliminates the insulating sheet between the reflector member and the printed circuit board. The flashlamps, which have long tubular envelopes, are arranged to lie horizontally and are stacked vertically as contrasted to the earlier flip flash unit which employed vertically oriented lamps arranged in two columns of four each. The overall dimensions of both types of arrays are approximately the same. In view of the modified reflector, however, the foil-lamanated indicia sheet is provided with folded side portions which extend from the back to the front along each side of the unit so as to provide additional electrostatic shielding.
U.S. Pat. No. 4,164,007 describes an improved multilamp photoflash unit which more efficiently utilizes a given housing volume and thereby reduces the cost of the unit per flash lamp contained therein. More specifically, a compact lamp arrangement is provided whereby additional lamps are contained in a given volume while maintaining light output performance requirements. In a particular embodiment described, ten lamps are provided in a housing having the same dimensions as the above-discussed eight-lamp flip flash units. This greater compactness is provided by arranging the planar array of lamps in two parallel columns with the tubular envelopes horizontally disposed and with the lamps of one column staggered with respect to the other such that the bases are interdigitated. A pair of reflector panels are aligned with the two columns of lamps and arranged to overlie the lamp lead-in wires and bases.
Another U.S. Patent, namely, U.S. Pat. No. 4,136,377, describes a foldable photoflash unit for avoiding the "red-eye" effect. In this instance, a linear array of lamps is provided in an elongated housing which pivots at one end, in jackknife fashion, from a mounting or support member inserted in a camera socket. The housing of this unit is illustrated as comprising a base, a light-transmitting cover, a printed circuit board, and a reflector member having a plurality of cavities in which the lamps are mounted. The lamps have tubular envelopes and are arranged with the longitudinal axis of the lamps normal to the longitudinal axis of the elongated housing. When the housing is pivoted outwardly for operation, the linear array of lamps are disposed in a horizontal row with each of the lamp envelopes oriented vertically.
Although each of the above-described photoflash devices provide satisfactory operation and useful means for overcoming the red-eye problem, the construction of all of the units is somewhat cumbersome and costly in terms of both materials and manufacturing assembly.
Other somewhat more compact photoflash array packages are described in U.S. Pat. Nos. 3,430,545 and 3,473,880 of Wick and Austrian Pat. No. 267323; however, none of these photoflash arrays appear suited for high-voltage type lamp operation due to lack of electrostatic shielding of the lamps and the circuitry, and none of the approaches contend with the red-eye problem. Both of the Wick patents show horizontal arrays of lamps in which the rear housing member also appears to integrally provide reflector cavities for each lamp and a circuit board substrate. A light-transmitting cover is attached to the front of the rear housing member. In U.S. Pat. No. 3,430,545, the switching appears to be accomplished in the camera, whereas in U.S. Pat. No. 3,473,880, the switching means is provided in each lamp, a feature which would appear to increase the cost and complexity of the photoflash lamps. The last mentioned Wick patent also illustrates an embodiment wherein horizontally oriented lamps are disposed in two vertical columns. The Austrian patent discloses two embodiments of a vertical linear array having a connector at one end. None of the units employs a printed circuit board. In one of the embodiments, each lamp is oriented diagonally and inserted in the socket of a supporting wall which provides reflectors for each lamp. The supporting wall-reflector-lamp assembly is enclosed in a tubular transparent container closed off at the top by a hemispherical cap and seated on a plastic base having a connector. In a second embodiment, the lamps of the array are oriented vertically along a common axis and mounted on a ladder-type support member within the tubular transparent cover. A portion of one wall of the tubular transparent cover may be coated with a reflecting layer.
The still-camera photography market is now about equally divided between conventional and instant picture type cameras. Significant advances in the speed of both the film and lenses for conventional cameras have reduced the light levels needed from a mating photoflash device. In contrast, many now popular instant picture cameras are preferably used with even brighter flash sources than flip flash. In order to meaningfully increase the photographically useful light from a conventional flip flash, for use with instant picture cameras, the number of lamps would have to be held at eight, or preferably even reduced to six (to permit, large efficient reflectors). The necessary prorating of the array component costs gives an unfavorable per flash cost with such six or eight lamp output enhanced flip flash arrays. Increasing the number of lamps to more than ten per array (as, for example, in a decreased output product for use with present high-speed films in conventional cameras) gives rise to high unit cost, crowding of the high voltage circuit board, and the problem of an unacceptable number of inaccessible good lamps if one earlier-firing lamp should fail.